1. Field of the Invention
The present invention relates to an optical information recording medium of the heat mode type having a recording layer disposed on a substrate and capable of recording information by exposure to a laser beam and a method of manufacturing such an optical information recording medium, and more particularly to an optical information recording medium whose recording layer can be inspected by an inspecting means and a method of manufacturing such an optical information recording medium.
2. Description of the Related Art
Optical information recording mediums (optical disks) capable of recording information once with a laser beam include a write-once CD (so-called CD-R) and a DVD-R. These optical information recording mediums are advantageous in that they allow a smaller quantity of CDs to be supplied quickly to the market at a reasonable price than conventional CDs (compact disks), and there are growing demands for such optical information recording mediums in view of the recent widespread use of personal computers.
Typically, a CD-R-type information recording medium comprises a disk-shaped transparent substrate having a thickness of about 1.2 mm, a recording layer of an organic dye deposited on the substrate, a light reflecting layer of metal such as gold or silver disposed on the recording layer, and a protective layer of resin disposed on the light reflecting layer.
A DVD-R-type information recording medium comprises two disk-shaped transparent substrates each having a thickness of about 0.6 which are bonded to each other with their information recording surfaces facing each other. The DVD-R-type information recording medium can record a greater amount of information.
Information can be written or recorded on these optical information recording mediums by applying a laser beam in a near-infrared range, e.g., a laser beam having a wavelength of about 780 nm for a CD-R or a laser beam having a wavelength of about 635 nm for a DVD-R, to the optical information recording mediums. When the laser beam is applied to an area of the dye recording layer, the irradiated area absorbs the applied laser beam and causes a local temperature rise, which produces a physical or chemical change, e.g., generates a pit, to change optical characteristics of the area of the dye recording layer for thereby recording the information.
Recorded information can be read or reproduced by applying a laser beam having the same wavelength as the wavelength of the recording laser beam. The recorded information is reproduced based on the detected difference between the reflectance of the area where the optical characteristics of the dye recording layer have been changed, i.e., a recorded area represented by the pit, and the area where the optical characteristics of the dye recording layer have not been changed, i.e., an unrecorded area.
If optical disks have a dye recording layer which suffers thickness irregularities, then those optical disks tend to cause a reading error and/or a recording error.
It is therefore an object of the present invention to provide an optical information recording medium of high quality which is produced through highly accurate inspection of the thickness of a recording layer formed on a substrate in the process of fabricating the optical information recording medium, and a method of manufacturing such an optical information recording medium.
According to the present invention, there is provided an optical information recording medium of the heat-mode type, comprising a substrate, and a recording layer disposed on the substrate for recording information upon exposure to a laser beam, the optical information recording medium being fabricated by inspecting a film thickness of the recording layer based on a detected signal from transmitted light detecting means for detecting a light beam having passed through the substrate, and inspecting a full amount of a light beam emitted from light applying means for applying the light beam to the substrate with the recording layer disposed thereon and an amount of light while the light beam emitted from the light applying means is being blocked by light shielding means for blocking the light beam emitted from the light applying means.
According to the present invention, there is also provided a method of manufacturing an optical information recording medium of the heat-mode type having a substrate, and a recording layer disposed on the substrate for recording information upon exposure to a laser beam, using film thickness inspecting means for inspecting a film thickness of the recording layer, the film thickness inspecting means having light applying means for applying the light beam to the substrate with the recording layer disposed thereon, transmitted light detecting means for detecting a light beam having passed through the substrate, and light shielding means for blocking the light beam emitted from the light applying means, the method comprising the steps of inspecting a film thickness of the recording layer based on a detected signal from the transmitted light detecting means, and inspecting a full amount of the light beam emitted from the light applying means and an amount of light while the light beam emitted from the light applying means is being blocked by the light shielding means.
With the above arrangement, it is possible to accurately inspect the film thickness of the recording layer on the substrate without being affected by ambient light such as light from fluorescent lamps, and reject any optical information recording mediums or optical disks with insufficient film thicknesses from a fabrication stage. Therefore, fabricated optical disks are prevented from suffering reading and recording errors.
The extinction coefficient of the light beam emitted from the light applying means at the complex index of refraction should preferably range from 0.2 to 1.2, more preferably range from 0.5 to 1.2, and most preferably range from 0.9 to 1.2.
Furthermore, there is also provided in accordance with the present invention a method of manufacturing an optical information recording medium of the heat-mode type having a substrate, and a recording layer disposed on the substrate for recording information upon exposure to a laser beam, using film thickness inspecting means for inspecting a film thickness of the recording layer, the film thickness inspecting means having light applying means for applying the light beam to the substrate with the recording layer disposed thereon, and transmitted light detecting means for detecting a light beam having passed through the substrate, the method comprising the steps of inspecting a film thickness of the recording layer based on a detected signal from the transmitted light detecting means, and setting an extinction coefficient of the light beam emitted from the light applying means to a value ranging from 0.2 to 1.2 at a complex index of refraction.
Thus, the relationship between optical densities of transmitted light determined from the transmittance of the light beam having passed through the recording layer and film thicknesses of the recording layer can be approximately represented by a linear function irrespectively of the type of a dye employed in the recording layer, thus allowing the film thickness to be measured easily and highly accurately.
The light beam emitted from the light applying means may comprise a flickering light beam. Preferably, the light applying means and the transmitted light detecting means are fabricated as a monolithic structure on a substrate. Since the light applying means and the transmitted light detecting means are subject to the same temperature, the film thickness of dye recording layer can be inspected with high accuracy without causing errors due to the ambient temperature. The substrate is preferably made of a semiconductor.
The film thickness inspecting means should preferably include an optical fiber for guiding the light beam emitted from the light applying means to the substrate and an optical fiber for guiding the light beam having passed through the substrate to the transmitted light detecting means.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which preferred embodiments of the present invention are shown by way of illustrative example.